Method of making a discharge lamp



Oct. 6, 1964 K. s. PREscHL-:L ETAL 3,151,922 y METHOD oF MAKING A DISCHARGE LAMP a I8/ E@ ITWSDTOT'S CLidl'F-Ord ONeiLL b9 T-hei fttoheg Henneft'h 5. PVeSCheL` Oct. 6, 1964 K. s. PREscHEL ETAL 3,151,922

METHOD oF MAKING A DISCHARGE LAMP Filed oct. 5, 1962 2 sheets-sheet 2 ITwVeTwToT-S: KennefL-h S. PT'eScheL CLifFfPoT-d F O eiYLL bg MW@ 7 M Theiv Afldovneg United States Patent O 3,151,922 MIETHD F MAKENG A DSCHARGE LA h'iP Kenneth S. Presehei, Warrensvilie Heights, and Cliiiord F. Oi Teill, Cleveland, Ohio, assignors to General Electric Company, a corporation of New York Filed Oct. 5, 1962, Ser. No. 228,695 Claims. (l. 31o-19) This invention relates generaly to discharge lamps and more particularly to a novel electrode subassernbly therefor and method of making said electrode subassembly and said lamp.

There is a generally recognized type of discharge lamp referred to as electrode stabilized or short arc or compact source. The electrode stabilized discharge lamp is one in which the distance between the two electrodes is small with respect to the distance between the electrodes and the wall of the lamp envelope. in the electrode stabilized lamp, as will be appreciated from the term itself, the arc between electrodes is held in its proper position by the relatively heavy current flow between relatively closely spaced electrodes. Therefore, if the arc Within the lamp is to be in proper relation to the lamp envelope, that is, centered within the lamp envelope, it is imperative that the electrodes be properly aligned within the lamp at the time the electrodes are sealed therein. -t is therefore an object of this invention to provide an improved electrode subassembly for an electrode stabilized discharge lamp which virtually eliminates any problems of misalignment of the two electrodes in the lamp.

Discharge lamps of the type with which this invention deals have normally been constructed by first sealing one of the electrodes in one end of the lamp envelope and then in a separate operation sealing the other electrode into the other end of the lamp envelope. ln some cases the exhaust and gas lling of the lamp have been made simultaneously with the sealing of the second electrode. lt is an object of this invention to improve on the above processes by providing a method by which an electrode stabilized discharge lamp may be made in which both electrodes are simultaneously sealed in both ends of the lamp. This has the obvious advantages of speed and is more economical. Thus, it is a further object of this invention to provide a method for making electrode stabilized lamps which is more economical and expeditious than those methods previously used.

Briefly, in accordance with the invention, there is provided an electrode subassembly for a discharge lmnp which comprises a rod of electrode material having two necked portions deiining a knock-out section and a pair of lamp electrodes connected by said knock-out portion. The electrode subassembly may be made by grinding two indentions into a rod to determine the size of the knockout portion and hence the spacing between electrodes. The electrode subassembly is pinch-sealed into an envelope and the knock-out portion is then removed. The lamp is then finished by exhausting, iilling with a gas and tipped olf in the customary manner.

Further objects and advantages of the invention will be found in the complete specification below and in the accompanying drawing wherein:

PEG. l illustrates a lamp of the type with which the invention generally is concerned;

FIGS. 2 to 4 show the electrode subassembly at various stages of manufacture, FIG. 4 showing the new electrode subassembly;

BGS. 5 to 9 show the various stages in the manufacture of the lamp in accordance with the invention.

In FlG. l a lamp of the electrode stabilized type is shown which comprises an envelope i and electrodes 2 and 3 pinch-sealed in the end portions of the envelope.

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The envelope may be of an ordinary lime glass but is usually quartz. In some cases where high Wall loadings are to be used during lamp operation, the envelope may be made of sapphire. The electrode 2 consists of a pointed rod i which in most cases will be commercial tungsten. However, thoriated tungsten, or other metals of suitably high melting temperature may also be used. rhe tungsten rod i is secured to a foil 5 which is in turn secured to a conductor lead-in Wire 6. The foil 5 and conductor lead-in wire 6 may be manufactured from a single piece of wire by flattening an end portion of the wire to form the foil portion 5. The foil portion 5 is secured in the pinch seal portion 7. Molybdenum is generally used for the foil and lead-in Wire because this metal has a similar enough coeicient of expansion to that of the quartz envelope l, thus forming a seal between the quartz and the molybdenum which is not likely to break due to elevated temperatures occurring during operation of the lamp. The other electrode 3 similarly consists of a tungsten rod S secured to a molybdenum foil 9 which is in turn secured to a molybdenum conductor lead-in wire it?. The foil 9 and lead-in i@ are secured in pinch seal portion il. The electrode 3 is provided with a tungsten wire overwind l2 to reduce its temperature thus minimizing the quantity of tungsten vaporized from the electrode during operation of the lamp. This over- Wind is normally provided on the anode of the lamp when designed for direct current operation. When the lamp is intended for operation on alternating current, a similar overwind may be placed on electrode 2. The lamp envelope contains a lling of, for example, Xenon gas at a pressure of about 5-25 atmospheres which filling is inserted after the lamp is exhausted and then sealed into the enevelope by the closing off of exhaust tip 13. if desired, the lamp may be filled with mercury and a starting gas such as arg-on and various metals or metallic halides to vary the color and lumen output of the lamp.

in accordance with the invention, the above lamp is manufactured with the use of the below disclosed novel electrode and method, portions of apparatus being shown schematically therewith by way of example. As shown in FIG. 2, a straight tungsten rod to be used for the two electrodes is shaped so as to have a center weakened, or knock-out portion i4.. The shaping is done by a turning or grinding process utilizing, for example, the grinding wheels i5 and rotating the tungsten rod relative thereto. As used herein, the term shaping will be used generically to include any form of material forming and is meant to include grinding, milling, turning, forging, etc. In practice it has been found that grinding in the necked portions is the most satisfactory process for shaping the electrode since the tungsten is rather brittle and does not easily lend itself to a turning or forging process. The shaped electrode structure then has secured thereto, for example, by spot welding, the molybdenum foil and molybdenum conductor lead-in wires as shown in FIG. 3. A tungsten overwind 12 may be provided on that electrode which is intended to be the anode in the finished lamp (FiG. 4) or overwinds may be provided on both electrode structures. While the manufacture of the electrode structure has been shown in three stages, it will be appreciated that these stages need not appear in the particular order shown. For example, the tungsten overwind and the molybdenum foil and lead-in wires may be secured to the tungsten rod before the electrodes are shaped with knock-out portion between them, or the three operations may be performed substantially simultaneously to form the electrode subassembly.

Thus, it will be seen that the electrode subassembly to be used in the manufacture of the electrode stabilized lamp shown in FIG. l comprises the tungsten electrodes 2 and 3, the electrode 3 yintended to be the anode of the lamp having a tungsten overwind 12. Secured to the tungsten electrodes 2 and 3 are the molybdenum foil portions 5 and 9 and the molybdenum conductor lead-in wire portions 6 and 10. Hov ever, instead of being two separate electrodes as in the inished lamp shown in FIG. 1, the electrode subassembly is a unitary structure connected together by a knock-out portion 14, the knock-out portion being attached to both electrodes 2 and 3 by necked or ,indented portions 14a. The electrode spacing in the iinished lamp will thus be determined by the position of the necked portions 14a of the electrode structure, and it is no longer necessary to depend upon close manufacturing techniques in the assembly process to control electrode spacing. The unitary electrode structure has the further advantage that the arc gap between electrodes will be centered within the envelope 1 so long as the conductor lead-in wires 6 and 10 are spaced outside the end of the envelope the same distance when the seals 7 and 11 are made. A still further advantage is that regardless of the angle the electrode structure takes with respect to the axis of the envelope the electrodes will be axially aligned with each other even though the electrodes may not lie exactly on the longitudinal axis of the envelope.

The electrode subassembly structure may then be inserted into an envelope having an exhaust tube 16 as shown in FIG. 5, the electrode subassembly being held generally axially within the envelope by suitable means. Heat is applied by burners 17 to each end to seal the glass to the molybdenum foils 5 and 9. As shown in FIGS. 6 and 6a pressure may then be applied by the forming members 18, although in some instances these forming members may not be necessary since the heat alone may be sulicient to collapse the glass onto the electrode subassembly so as to form the pinch seals 7 and 11.

The envelope is usually provided with exhaust tube 16 prior to the sealing of the electrode structures therein, although this exhaust tube may be secured to the envelope 1 after the electrode subassembly is sealed into the envelope. The electrode subassembly being secured in the envelope with the electrodes 2 and 3 in direct alignment, the knock-out center portion 14 may be removed by various means. As shown inv FIG. 7, a mechanical means 19, such as a rod, may be used which is extended into the exhaust tube and disengages the knock-out from the two electrode portions. It should be noted that tungsten is relatively brittle and generally a light tap or vibration from the mechanical push-out means 19 is sufficient to disengage the knock-out portion 14 from the two electrodes. It has been found that imparting a longitudinal vibration to means 19 facilitates removal of portion 14. In some cases it may be desirable to use electrical, thermal, or chemical means to remove the knock-out portion from the lamp. For example, an inert gas may be inserted into the envelope through the exhaust tube and suliicient electric current run through the electrode structure to melt the necked-out portions of the electrode structure permitting the knock-out portion to drop from the complete electrode structure. In some cases, heat applied to the outside of the envelope may also be suficient to rupture the necked-out portions and cause the knock-out to drop. A further method of removing the knock-out might be to use chemical etching. While all of the above methods of removing the knock-out portion may be used, the latter two are least desirable since the heat applied to the exterior of the envelope necessary to melt the necked-out portion of the knock-out generally will tend to deform the glass envelope and chemical etching may leave undesirable contaminants within the lamp envelope. For these reasons that use of a mechanical means to remove the knock-out or an electric current through the electrode structure itself is preferred.

In any case, whatever method is used to cause the knock-out portion to disengage itself from the electrode structure, the knock-out portion being centered above the exhaust tube causes it to fall out through the exhaust tube when it becomes disengaged (FIG. 8). While it is generally desirable to remove the knock-out portion from the lamp envelope after it is disengaged from the electrode structure, it may not always be necessary and therefore the lamp may be exhausted and filled with the proper gas lling prior to an electric current being applied to the lamp electrodes so as to disengage the knockout portion.

As shown in FIG. 9 the lamp with the electrodes properly positioned in the pinch seals at the ends of the lamp may then be exhausted and iilled with a xenon, or other, gas lling through tube 20 and tipped oi'rr by burners 21 in the conventional manner.

While the invention has been disclosed with reference to electrode stabilized discharge lamp, it will be appreciated that it may iind application in any lamp manufacture wherein it is necessary to maintain alignment to the internal electrode structure.

What we claim as new and desire to be secured by Letters Patent of the United States is:

1. A method of making a subassembly for a discharge lamp comprising the steps of grinding two indented portions into a rod of electrode material thereby forming two electrodes connected by a knock-out portion and welding a pair of conductor leadain wires to either end of said rod.

2. A method of making a discharge lamp comprising the steps of sealing an electrode subassembly which comprises a pair of electrodes connected by a knock-out portion into a lamp envelope; removing said knock-out portion from between said electrodes after said electrode assembly is sealed into said envelope; exhausting said lamp envelope; iilling said lamp envelope with gas; and tipping oi the lamp.

3. A method of manufacturing a discharge lamp comprising the steps of shaping a rod of electrode materiaal to form a pair of electrodes connected together by a knock-out portion; securing conductor lead-in wires to the end of said rod; sealing said rod and said conductor lead-in wires into a glass envelope; removing the knockout portion from between the electrodes after said subassembly is secured in the envelope; and exhausting, iill- Y ing and tipping oi the lamp.

4. A method of manufacturing a lamp comprising the steps of grinding indented portions into a tungsten rod to form a pair of electrodes connected together by a knock-out portion; Welding conductor lead-in wires to the ends of said rod; sealing said conductor lead-in wires into the end of a lamp envelope with the knock-out portion connecting said electrodes; removing said knock-out portion from between said electrodes and from the interior of the lamp envelope; exhausting said envelope; illing said envelope with xenon gas; and tipping o said envelope.

5. A method of making a discharge lamp comprising the steps of sealing an electrode subassembly which cornprises a pair of tungsten electrodes connected together by a knock-out portion into a lamp envelope; removing said knock-out portion after said subassembly is sealed into said envelope; exhausting said envelope; lling said envelope with an inert gas and tipping off the lamp.

References Cited in the iile of this patent UNITED STATES PATENTS 1,788,437 McFarlin Ian. 13, 1931 2,194,652 Freedman Mar. 26, 1940 2,651,100 Grouse Sept. 8, 1953 

1. A METHOD OF MAKING A SUBASSEMBLY FOR A DISCHARGE LAMP COMPRISING THE STEPS OF GRINDING TWO INDENTED PORTIONS INTO A ROD OF ELECTRODE MATERIAL THEREBY FORMING TWO ELECTRODES CONNECTED BY A KNOCK-OUT PORTION AND WELDING A PAIR OF CONDUCTOR LEAD-IN WIRES TO EITHER END OF SAID ROD. 